Third generation (3G) mobile systems, such as, for instance, universal mobile telecommunication systems (UMTS) standardized within the third generation partnership project (3GPP) have been based on wideband code division multiple access (WCDMA) radio access technology. Today, 3G systems are being deployed on a broad scale all around the world. After enhancing this technology by introducing high-speed downlink packet access (HSDPA) and an enhanced uplink, also referred to as high-speed uplink packet access (HSUPA), the next major step in evolution of the UMTS standard has brought the combination of orthogonal frequency division multiplexing (OFDM) for the downlink and single carrier frequency division multiplexing access (SC-FDMA) for the uplink. This system has been named long term evolution (LTE) since it has been intended to cope with future technology evolutions.
The LTE system represents efficient packet based radio access and radio access networks that provide full IP-based functionalities with low latency and low cost. The detailed system requirements are given in 3GPP TR 25.913, “Requirements for evolved UTRA (E-UTRA) and evolved UTRAN (E-UTRAN),” v8.0.0, January 2009, (available at http://www.3gpp.org/ and incorporated herein by reference). The Downlink will support data modulation schemes QPSK, 16QAM, and 64QAM and the Uplink will support BPSK, QPSK, 8PSK and 16QAM.
LTE's network access is to be extremely flexible, using a number of defined channel bandwidths between 1.25 and 20 MHz, contrasted with UMTS terrestrial radio access (UTRA) fixed 5 MHz channels. Spectral efficiency is increased by up to four-fold compared with UTRA, and improvements in architecture and signalling reduce round-trip latency. Multiple Input/Multiple Output (MIMO) antenna technology should enable 10 times as many users per cell as 3GPP's original WCDMA radio access technology. To suit as many frequency band allocation arrangements as possible, both paired (frequency division duplex FDD) and unpaired (time division duplex TDD) band operation is supported. LTE can co-exist with earlier 3GPP radio technologies, even in adjacent channels, and calls can be handed over to and from all 3GPP's previous radio access technologies.
FIG. 1 illustrates structure of a component carrier in LTE Release 8. The downlink component carrier of the 3GPP LTE Release 8 is sub-divided in the time-frequency domain in so-called sub-frames each of which is divided into two downlink slots 120 corresponding to a time period Tslot. The first downlink slot comprises a control channel region within the first OFDM symbol(s). Each sub-frame consists of a given number of OFDM symbols in the time domain, each OFDM symbol spanning over the entire bandwidth of the component carrier. The smallest unit of resources that can be assigned by a scheduler is a resource block 130 also called physical resource block (PRB). A PRB 130 is defined as NsymbDL consecutive OFDM symbols in the time domain and NscRB consecutive sub-carriers in the frequency domain. In practice, the downlink resources are assigned in resource block pairs. A resource block pair consists of two resource blocks. It spans NscRB consecutive sub-carriers in the frequency domain and the entire 2·NsymbDL modulation symbols of the sub-frame in the time domain. NsymbDL may be either 6 or 7 resulting in either 12 or 14 OFDM symbols in total. Consequently, a physical resource block 130 consists of NsymbDL×NscRB resource elements 140 corresponding to one slot in the time domain and 180 kHz in the frequency domain (further details on the downlink resource grid can be found, for example, in 3GPP TS 36.211, “Evolved universal terrestrial radio access (E-UTRA); physical channels and modulations (Release 8)”, version 8.9.0, December 2009, Section 6.2, available at http://www.3gpp.org. which is incorporated herein by reference).
The number of physical resource blocks NRBDL in downlink depends on the downlink transmission bandwidth configured in the cell and is at present defined in LTE as being from the interval of 6 to 110 PRBs.
The data are mapped onto physical resource blocks by means of pairs of virtual resource blocks. A pair of virtual resource blocks is mapped onto a pair of physical resource blocks. The following two types of virtual resource blocks are defined according to their mapping on the physical resource blocks in LTE downlink:                Localised Virtual Resource Block (LVRB)        Distributed Virtual Resource Block (DVRB)        
In the localised transmission mode using the localised VRBs, the eNB has full control which and how many resource blocks are used, and should use this control usually to pick resource blocks that result in a large spectral efficiency. In most mobile communication systems, this results in adjacent physical resource blocks or multiple clusters of adjacent physical resource blocks for the transmission to a single user equipment, because the radio channel is coherent in the frequency domain, implying that if one physical resource block offers a large spectral efficiency, then it is very likely that an adjacent physical resource block offers a similarly large spectral efficiency. In the distributed transmission mode using the distributed VRBs, the physical resource blocks carrying data for the same UE are distributed across the frequency band in order to hit at least some physical resource blocks that offer a sufficiently large spectral efficiency, thereby obtaining frequency diversity.
In 3GPP LTE Release 8 there is only one component carrier in uplink and downlink. Downlink control signalling is basically carried by the following three physical channels:                Physical control format indicator channel (PCFICH) for indicating the number of OFDM symbols used for control signalling in a sub-frame (i.e. the size of the control channel region);        Physical hybrid ARQ indicator channel (PHICH) for carrying the downlink ACK/NACK associated with uplink data transmission; and        Physical downlink control channel (PDCCH) for carrying downlink scheduling assignments and uplink scheduling assignments.        
The PCFICH is sent from a known position within the control signalling region of a downlink sub-frame using a known pre-defined modulation and coding scheme. The user equipment decodes the PCFICH in order to obtain information about a size of the control signalling region in a sub-frame, for instance, the number of OFDM symbols. If the user equipment (UE) is unable to decode the PCFICH or if it obtains an erroneous PCFICH value, it will not be able to correctly decode the L1/L2 control signalling (PDCCH) comprised in the control signalling region, which may result in losing all resource assignments contained therein.
The PDCCH carries control information, such as, for instance, scheduling grants for allocating resources for downlink or uplink data transmission. A physical control channel is transmitted on an aggregation of one or several consecutive control channel elements (CCEs). Each CCE corresponds to a set of resource elements grouped to so-called resource element groups (REG). A control channel element typically corresponds to 9 resource element groups. A scheduling grant on PDCCH is defined based on control channel elements (CCE). Resource element groups are used for defining the mapping of control channels to resource elements. Each REG consists of four consecutive resource elements excluding reference signals within the same OFDM symbol. REGs exist in the first one to four OFDM symbols within one sub-frame. The PDCCH for the user equipment is transmitted on the first of either one, two or three OFDM symbols according to PCFICH within a sub-frame.
Another logical unit used in mapping of data onto physical resources in 3GPP LTE Release 8 (and later releases) is a resource block group (RBG). A resource block group is a set of consecutive (in frequency) physical resource blocks. The concept of RBG provides a possibility of addressing particular RBGs for the purpose of indicating a position of resources allocated for a receiving node (e.g. UE), in order to minimise the overhead for such an indication, thereby decreasing the control overhead to data ratio for a transmission. The size of RBG is currently specified to be 1, 2, 3, or 4, depending on the system bandwidth, in particular, on NRBDL. Further details of RBG mapping for PDCCH in LTE Release 8 may be found in 3GPP TS 36.213 “Evolved Universal terrestrial Radio Access (E-UTRA); Physical layer procedures”, v8.8.0, September 2009, Section 7.1.6.1, freely available at http://www.3gpp.org/ and incorporated herein by reference.
Physical downlink shared channel (PDSCH) is used to transport user data. PDSCH is mapped to the remaining OFDM symbols within one sub-frame after PDCCH. The PDSCH resources allocated for one UE are in the units of resource block for each sub-frame.
FIG. 2 shows an exemplary mapping of PDCCH and PDSCH within a sub-frame. The first two OFDM symbols form a control channel region (PDCCH region) and are used for L1/L2 control signalling. The remaining twelve OFDM symbols form data channel region (PDSCH region) and are used for data. Within a resource block pairs of all sub-frames, cell-specific reference signals, so-called common reference signals (CRS), are transmitted on one or several antenna ports 0 to 3. In the example of FIG. 2, the CRS are transmitted from two antenna ports: R0 and R1. Moreover, the sub-frame also includes UE-specific reference signals, so-called demodulation reference signals (DM-RS) used by the user equipment for demodulating the PDSCH. The DM-RS are only transmitted within the resource blocks in which the PDSCH is allocated for a certain user equipment. In order to support multiple input/multiple output (MIMO) with DM-RS, four DM-RS layers are defined meaning that at most, MIMO of four layers is supported. In this example, in FIG. 2, DM-RS layer 1, 2, 3 and 4 are corresponding to MIMO layer 1, 2, 3 and 4.
One of the key features of LTE is the possibility to transmit multicast or broadcast data from multiple cells over a synchronized single frequency network which is known as multimedia broadcast single frequency network (MBSFN) operation. In MBSFN operation, UE receives and combines synchronized signals from multiple cells. To facilitate this, UE needs to perform a separate channel estimation based on an MBSFN reference signal. In order to avoid mixing the MBSFN reference signal and normal reference signal in the same sub-frame, certain sub-frames known as MBSFN sub-frames are reserved from MBSFN transmission.
The structure of an MBSFN sub-frame is shown in FIG. 3 up to two of the first OFDM symbols are reserved for non-MBSFN transmission and the remaining OFDM symbols are used for MBSFN transmission. In the first up to two OFDM symbols, PDCCH for uplink resource assignments and PHICH can be transmitted and the cell-specific reference signal is the same as non-MBSFN transmission sub-frames. The particular pattern of MBSFN sub-frames in one cell is broadcasted in the system information of the cell. UEs not capable of receiving MBSFN will decode the first up to two OFDM symbols and ignore the remaining OFDM symbols. MBSFN sub-frame configuration supports both 10 ms and 40 ms periodicity. However, sub-frames with number 0, 4, 5 and 9 cannot be configured as MBSFN sub-frames. FIG. 3 illustrates the format of an MBSFN subframe. The PDCCH information sent on the L1/L2 control signalling may be separated into the shared control information and dedicated control information.
The frequency spectrum for IMT-advanced was decided at the World Radio Communication Conference (WRC-07) in November 2008. However, the actual available frequency bandwidth may differ for each region or country. The enhancement of LTE standardized by 3GPP is called LTE-advanced (LTE-A) and has been approved as the subject matter of Release 10. LTE-A Release 10 employs carrier aggregation according to which two or more component carriers as defined for LTE Release 8 are aggregated in order to support wider transmission bandwidth, for instance, transmission bandwidth up to 100 MHz. More details on carrier aggregation can be found in 3GPP TS 36.300 “Evolved Universal terrestrial Radio Access (E-UTRA) and Universal terrestrial Radio Access Network (E-UTRAN); Overall description”, v10.2.0, December 2010, Section 5.5 (Physical layer), Section 6.4 (Layer 2) and Section 7.5 (RRC), freely available at http://www.3gpp.org/ and incorporated herein by reference. It is commonly assumed that the single component carrier does not exceed a bandwidth of 20 MHz. A terminal may simultaneously receive and/or transmit on one or multiple component carriers depending on its capabilities. A UE may be configured to aggregate a different number of component carriers (CC) in the uplink and in the downlink. The number of downlink CCs which can be configured depends on the downlink aggregation capability of the UE. The number of uplink CCs which can be configured depends on the uplink aggregation capability of the UE. However, it is not possible to configure a UE with more uplink CCs than downlink CCs.
The term “component carrier” is sometimes replaces with the term “cell” since, similar to a concept of a cell known from earlier releases of LTE and UMTS, a component carrier defines resources for transmission/reception of data and may be added/reconfigures/removed from the resources utilized by the wireless nodes (e.g. UE, RN). In particular, a cell is a combination of downlink and optionally uplink resources, i.e. downlink and optional uplink component carrier. In Rel-8/9, there are one carrier frequency of downlink resources and one carrier frequency of uplink resources. The carrier frequency of downlink resources is detected by UE through cell selection procedure. The carrier frequency of uplink resources is informed to UE through System Information Block 2. When carrier aggregation is configured, there are more than one carrier frequency of downlink resources and possibly more than one carrier frequency of uplink resources. Therefore, there would be more than one combination of downlink and optionally uplink resources, i.e. more than one serving cell. The primary serving cell is called Primary Cell (PCell). Other serving cells are called Secondary Cells (SCells).
When carrier aggregation is configured, a UE has only one Radio Resource Control (RRC) connection with the network. Primary Cell (PCell) provides the non-access stratum (NAS) mobility information and security input at RRC connection reestablishment or handover. Depending on UE capabilities, Secondary Cells (SCells) can be configured to form together with the PCell a set of serving cells. RRC connection is the connection between RRC layer on UE side and RRC layer on network side. Establishment, maintenance and release of an RRC connection between the UE and E-UTRAN include: allocation of temporary identifiers between UE and E-UTRAN; configuration of signalling radio bearer(s) for RRC connection, i.e., Low priority SRB and high priority SRB. More details on RRC can be found in 3GPP TS 36.331 “Evolved Universal terrestrial Radio Access (E-UTRA); Radio Resource Control (RRC); Protocol specification”, v10.0.0, December 2010, freely available at http://www.3gpp.org/ and incorporated herein by reference.
In the downlink, the carrier corresponding to PCell is called Downlink Primary Component Carrier (DL PCC) whereas in the uplink, the carrier corresponding to PCell is called Uplink Primary Component Carrier (UL PCC). The linking between DL PCC and UL PCC is indicated in the system information (System Information Block 2) from the PCell. System information is common control information broadcast by each cell, including, for instance, information about the cell to the terminals. With regard to the system information reception for the PCell, the procedure of LTE in Rel-8/9 applies. The details on system information reception procedure for Rel-8/9 can be found in 3GPP TS 36.331 “Evolved Universal terrestrial Radio Access (E-UTRA); Radio Resource Control (RRC); Protocol specification”, v9.5.0, December 2010, Section 5.2, freely available at http://www.3gpp.org/ and incorporated herein by reference. In the downlink, the carrier corresponding to an SCell is a Downlink Secondary Component Carrier (DL SCC) while in the uplink it is an Uplink Secondary Component Carrier (UL SCC). The linking between DL SCC and UL SCC is indicated in the system information (System Information Block 2) of the SCell. All required system information of the SCell is transmitted to UE through dedicated RRC signalling when adding an SCell. Hence, there is no need for the UE to acquire system information directly from SCells. The system information of an SCell remains valid as long as the SCell is configured. Changes in system information of an SCell are handled through the removal and addition of the SCell. Removal and/or addition of an SCell can be performed using an RRC procedure.
Both downlink grant and uplink grant are received on DL CC. Therefore, in order to know the uplink grant received on one DL CC corresponds to the uplink transmission of which UL CC, the linking between DL CC and UL CC would be necessary.
A linking between UL CC and DL CC allows identifying the serving cell for which the grant applies:                downlink assignment received in PCell corresponds to downlink transmission in the PCell,        uplink grant received in PCell corresponds to uplink transmission in the PCell,        downlink assignment received in SCellN corresponds to downlink transmission in the SCellN,        uplink grant received in SCellN corresponds to uplink transmission in the SCellN. If SCellN is not configured for uplink usage by the UE, the grant is ignored by the UE.        
3GPP TS 36.212 v10.0.0, also describes in Section 5.3.3.1 the possibility of cross-carrier scheduling, using a Carrier Indication Field (CIF).
UE may be scheduled over multiple serving cells simultaneously. A cross-carrier scheduling with a CIF allows the PDCCH of a serving cell to schedule resources in another serving cell(s), however, with the following restrictions:                cross-carrier scheduling does not apply to PCell, which means that PCell is always scheduled via its own PDCCH,        when the PDCCH of a secondary cell (SCell) is configured, cross-carrier scheduling does not apply to this SCell, which means that the SCell is always scheduled via its own PDCCH, and        when the PDCCH of an SCell is not configured, cross-carrier scheduling applies and such SCell is always scheduled via PDCCH of another serving cell.        
Therefore, if there is no CIF, the linking between DL CC and UL CC identifies the UL CC for uplink transmission; if there is CIF, the CIF value identifies the UL CC for uplink transmission.
The set of PDCCH candidates to monitor, where monitoring implies attempting to decode each of the PDCCHs, are defined in terms of search spaces. A UE not configured with a Carrier Indicator Field (CIF) shall monitor one UE-specific search space at each of the aggregation levels 1, 2, 4, 8 on each activated serving cell. A UE configured with a Carrier Indicator Field (CIF) shall monitor one or more UE-specific search spaces at each of the aggregation levels 1, 2, 4, 8 on one or more activated serving cells. If a UE is configured with a CIF, the UE specific search space is determined by the component carrier, which means that the indices of CCEs corresponding to PDCCH candidates of the search space are determined by the Carrier Indicator Field (CIF) value. The carrier indicator field specifies an index of a component carrier.
If a UE is configured to monitor PDCCH candidates in a given serving cell with a given DCI format size with CIF, the UE shall assume that a PDCCH candidate with the given DCI format size may be transmitted in the given serving cell in any UE specific search space corresponding to any of the possible values of CIF for the given DCI format size. It means that if one given DCI format size can have more than one CIF value, UE shall monitor the PDCCH candidates in any UE specific search spaces corresponding to any possible CIF value with that given DCI format.
Further details on configurations of search spaces with and without CIF as defined in LTE-A for PDCCH can be found in 3GPP TS 36.213 “Evolved Universal terrestrial Radio Access (E-UTRA); Physical Layer procedures”, v10.0.0, December 2010, Section 9.1.1, freely available at http://www.3gpp.org/ and incorporated herein by reference.
Another key feature of the LTE-A is providing relaying functionality by means of introducing relay nodes to the UTRAN architecture of 3GPP LTE-A. Relaying is considered for LTE-A as a tool for improving the coverage of high data rates, group mobility, temporary network deployment, the cell edge throughput and/or to provide coverage in new areas.
A relay node is wirelessly connected to radio access network via a donor cell. Depending on the relaying strategy, a relay node may be part of the donor cell or, alternatively, may control the cells on its own. In case the relay node is a part of the donor cell, the relay node does not have a cell identity on its own, however, may still have a relay ID. In the case the relay node controls cells on its own, it controls one or several cells and a unique physical layer cell identity is provided in each of the cells controlled by the relay. At least, “type 1” relay nodes will be a part of 3GPP LTE-A. A “type 1” relay node is a relaying node characterized by the following:                The relay node controls cells each of which appears to a user equipment as a separate cell distinct from the donor cell.        The cells should have its own physical cell ID as defined in LTE Release 8 and the relay node shall transmit its own synchronization channels, reference symbols etc.        Regarding the single cell operation, the UE should receive scheduling information and HARQ feedback directly from the relay node and send its controlled information (acknowledgments, channel quality indications, scheduling requests) to the relay node.        The relay node should appear as a 3GPP LTE compliant eNodeB to 3GPP LTE compliant user equipment in order to support the backward compatibility.        The relay node should appear differently to the 3GPP LTE eNodeB in order to allow for further performance enhancements to the 3GPP LTE-A compliant user equipments.        
FIG. 4 illustrates an example 3GPP LTE-A network structure using relay nodes. A donor eNodeB (d-eNB) 410 directly serves a user equipment UE1 415 and a relay node (RN) 420 which further serves UE2 425. The link between donor eNodeB 410 and the relay node 420 is typically referred to as relay backhaul uplink/downlink. The link between the relay node 420 and user equipment 425 attached to the relay node (also denoted r-UEs) is called (relay) access link.
The donor eNodeB transmits L1/L2 control and data to the micro-user equipment UE1 415 and also to a relay node 420 which further transmits the L1/L2 control and data to the relay-user equipment UE2 425. The relay node may operate in a so-called time multiplexing mode, in which transmission and reception operation cannot be performed at the same time. In particular, if the link from eNodeB 410 to relay node 420 operates in the same frequency spectrum as the link from relay node 420 to UE2 425, due to the relay transmitter causing interference to its own receiver, simultaneous eNodeB-to-relay node and relay node-to-UE transmissions on the same frequency resources may not be possible unless sufficient isolation of the outgoing and incoming signals is provided. Thus, when relay node 420 transmits to donor eNodeB 410, it cannot, at the same time, receive from UEs 425 attached to the relay node. Similarly, when a relay node 420 receives data from donor eNodeB, it cannot transmit data to UEs 425 attached to the relay node. Thus, there is a sub-frame partitioning between relay backhaul link and relay access link.
Regarding the support of relay nodes, in 3GPP it has currently been agreed that:                Relay backhaul downlink sub-frames during which eNodeB to relay downlink backhaul transmission is configured, are semi-statically assigned.        Relay backhaul uplink sub-frames during which relay-to-eNodeB uplink backhaul transmission is configured are semi-statically assigned or implicitly derived by HARQ timing from relay backhaul downlink sub-frames.        In relay backhaul downlink sub-frames, a relay node will transmit to donor eNodeB and consequently r-UEs are not supposed to expect receiving any data from the relay node. In order to support backward compatibility for UEs that are not aware of their attachment to a relay node (such as Release 8 UEs for which a relay node appears to be a standard eNodeB), the relay node configures backhaul downlink sub-frames as MBSFN sub-frames.        
Another key feature is the FDD (Frequency Division Duplex) HARQ-ACK procedure. For FDD, if UE detects PDSCH in subframe n−4 intended for the UE and a HARQ-ACK shall be provided, UE shall transmit the HARQ-ACK response in subframe n. The number of HARQ-ACK bits to be transmitted depends on the number of configured serving cells and the downlink transmission mode of each configured cells. If the downlink transmission mode of a serving cell supports up to two transport blocks, two HARQ-ACK bits is used by a UE, otherwise one HARQ-ACK bit.
For FDD, a UE supports at most 2 serving cells shall use PUCCH format 1b with channel selection for transmission of HARQ-ACK when configured with more than one serving cells.
For FDD, a UE that supports more than 2 serving cells use either use PUCCH format 1b with channel selection for PUCCH format 3 for transmission of HARQ-ACK when configured with more than one serving cell.
In case of FDD and one configured cell, the UE shall use PUCCH format 1a/1b to transmit HARQ-ACK. If the downlink transmission mode of the configured serving cell supports up to two transport block, PUCCH format 1b is used, otherwise PUCCH format 1a is used.
The PUCCH resource is determined either by the first CCE index of corresponding PDCCH or by higher layer configuration. If PDSCH transmission is detected with a corresponding PDCCH, the PUCCH resource is determined by the first CCE index of the corresponding PDCCH, otherwise, the PUCCH resource is determined by higher layer configuration.
In case of FDD and the UE being configured with more than one serving cells, the HARQ-ACK is either transmitted using PUCCH format 1b with channel selection or using PUCCH format 3. The detailed information can be found in 3GPP, TS 36.213, “Evolved Universal Terrestrial Radio Access (E-UTRA); Physical layer procedures (Release 10)”, freely available at www.3gpp.org and incorporated herein by reference.
Depending on the downlink transmission mode of each configured serving cell, A (A=2, 3, 4) HARQ-ACK bits need to be transmitted. The UE transmits the HARQ-ACK bits using PUCCH format 1b with b(0)b(1) on one PUCCH resource selected from A PUCCH resources. The A PUCCH resources are derived from the first CCE index of corresponding PDCCH or determined from higher layer configuration. The detailed mapping tables are defined in 3GPP, TS 36.213, “Evolved Universal Terrestrial Radio Access (E-UTRA); Physical layer procedures (Release 10)”, freely available at www.3gpp.org and incorporated herein by reference.
For FDD, if UE is configured with PUCCH format 3, UE shall transmit HARQ-ACK on one PUCCH resource according to following rules:                If PDSCH transmission is only detected on primary cell, UE shall use PUCCH format 1a/1b to transmit HARQ-ACK on one PUCCH resource. The PUCCH resource is derived from the first CCE index of corresponding PDCCH or from higher layer configuration.        If PDSCH transmission is detected on secondary cell, PUCCH format 3 is used to transmit HARQ-ACK on one PUCCH resource. The TPC field in DCI format of the corresponding PDCCH shall be used to determine the PUCCH resource selected from the PUCCH resources configured by higher layer.        
For FDD, in PUCCH format 3, HARQ-ACK bits from different configured serving cells are concatenated.
Another key feature is the Enhanced PDCCH (E-PDCCH), which is transmitted based on UE specific reference signal. In order to efficiently use UE specific reference signal, the mapping of enhanced PDCCH is preferred to be allocated in PDSCH region. In order not to blind decode the whole bandwidth, it is assumed that the search space of E-PDCCH would be limited within a set of PRBs. The set of PRBs is first configured by higher layer signalling.
However, in certain scenarios, fast reconfiguration of the search space of E-PDCCH is necessary, for example, if the interference from neighbouring cells change on a timescale of 10 ms. Since E-PDCCH is transmitted in PDSCH region, the interference mainly comes from PDSCH transmission in neighbouring cells. In order to introduce more stable interference pattern to neighbouring cell, it is assumed that the PMI (beam) of neighbouring cells changes in the order of 10 ms. In this case, the flash light interference to E-PDCCH, i.e. the interference from the beam of PDSCH transmission to E-PDCCH, can be avoided by fast reconfiguration of the search space of E-PDCCH in the order of 10 ms. The flashlight interference from neighboring cells is illustrated in FIG. 5.
Another example is a frequency fluctuation dominated scenario, e.g. on low interference subframe of pico cell, fast reconfiguration of the search space of E-PDCCH can achieve better frequency scheduling gain by allocating the search space of E-PDCCH on best PRBs.
Hence, from above scenarios it is apparent that a fast reconfiguration of the search space of E-PDCCH in the order of 10 ms is mandatory.
A straightforward solution is to reconfigure the search space of E-PDCCH by higher layer signalling. This solution, however, has the drawback that higher layer signalling is too slow. The delay of higher layer signalling is in the order of 100 ms, while fast reconfiguration of the search space of E-PDCCH in the order of 10 ms is necessary. Moreover, higher layer signalling has a large overhead. Since the reconfiguration is frequent, using higher layer signalling costs lots of resources.